Generally, seats, chairs, rockers and for that matter any device intended to pivot or rock relative to a base, conventionally uses metal coil springs to create torsional resistance to the rocking motion. To increase or decrease the degree of stiffness of the spring, mechanisms are usually employed to change the torsional properties of the spring by twisting or compressing the spring or otherwise changing its shape.
While the desired results of torsional adjustability usually have been obtained, it has not been without ancillary problems. Friction occurs between the spring and the adjusting mechanism (usually metal) used to compress or twist it. Lubrication is required, not only to reduce friction, but also to prevent squeaking. The mechanisms are frequently complex and often costly to manufacture.
Another problem with springs which require their shape to be changed to vary their torsional properties is that considerable force is necessary to deform the spring. Hand wheels, levers, and cams used for this purpose require considerable manual strength to operate, often more than can be summoned, if the user is of advanced age or is infirm.
Accordingly, one of the objects of this invention is to produce an adjustable torsion spring, the torsional properties of which may be varied with little human effort being required.
Another object of the invention is to produce an adjustable torsion spring which is relatively frictionless and requires little or no lubrication.
Yet another object is to produce a simple, inexpensive adjustable spring, the torsional properties of which may be changed without changing the shape of the spring.